Mantle COH‐Rich Magmatic Lineage Tree Traces Thermochemical Change and REE Refertilisation in Continental Roots

ABSTRACT

Continental roots are the ultimate sources for many giant metal deposits including rare‐earth elements (REEs). The ore‐fertile magmatic rocks inherently have undergone complex evolution, making metal pre‐enrichment processes in the mantle sources poorly understood. Co‐existing carbonatites and other COH‐rich magmatic rocks like kimberlites and lamproites in many polymetallic mineralisation areas likely represent different branches of similar COH‐rich mantle melt precursors. Such volatile‐rich melts are argued to have involved substantial mass contribution from a MARID (M‐Mica, A‐amphibole, R‐Rutile, I‐ilmenite and D‐diopside)‐rich mid‐lithospheric layer. Melting of this critical layer could be triggered by asthenospheric upwelling associated with lithospheric thinning under cratonic margins, giving rise to continental magmatism rich in COH volatiles, REEs, Fe and Nb. Taken the world's largest REE deposit at Bayan Obo area (northern North China Craton) as an example, natural outcrops and drilling samples from the Ultra‐Deep Scientific Deep Drilling Project jointly offers an unprecedent opportunity to establish the COH‐rich magmatic lineage tree; systematic research on these magmatic rocks and the entrained xenolithic suites enables the reconstruction of regional lithospheric thickness and thermochemical profile and ultimately allows for careful characterisation on the mineralisation processes from source pre‐enrichment to magmatic differentiation.